Thursday, March 27, 2014

Krueger-HVAC Response to ASHRAE Journal Article on "Hospital OR Air Distribution"

In February, there was an ASHRAE Journal article on Hospital OR Air Distribution. After thoroughly reviewing it, we identified several technical flaws. It’s worth noting that the article I authored on the same subject was published in December 2013 (with quite different conclusions, I might add). Now with 11 articles having been accepted by the Journal as of recent, only a few are posted on our website, unfortunately. We will make them available as soon as we get approved copies from ASHRAE.

In response to the article, a letter to the editor was prepared by our Engineering Manager and will hopefully be published soon. Below is a quick summary of what was sent:

Summary of letter to the editor on “Improving Operating Room Contamination Control”

  1. The authors incorrectly state the four different ceiling air delivery scenarios meet ASHRAE Standard 170 guidelines for diffuser coverage over the patient table.
  2. The AC system doesn’t comply with the Space Ventilation requirements stated in section 7.1.a of ASHRAE Standard 170-2013.
  3. Based on the sizing of the AC system, one could also question the results for the MDA system.
  4. Splitting the MDA array completely across the table is one of the worst possible configurations for this type of system, especially since it happens right in the middle of the surgical table where it can induce contaminants rising from the patient.
  5. The author gives the room dimensions as 20 ft 5 in. W x 20 ft 7 in. L x 10 ft H for a room volume of 4,202 ft3 but uses a room volume of 4,800 ft3 to 4,822 ft3 for their ACH calculations.
  6. The author makes the statement – “The data also indicates that at equal size and airflow, a one or two ISO Class improvement was achieved between the MDA and SLD1 scenarios without additional energy consumption.” The data shows only a single ISO Class Improvement from ISO Class 8 for the MDA-30 to an ISO Class 7 for the SLD1-30 for systems complying with ASHRAE Standard 170-2013.

While this article is a good starting point for generating dialog on hospital OR environments, the study itself is flawed and looks to be more of a marketing/promotional piece for manufacturers of SLD systems.

The results are at odds with both the testing conducted by Krueger in the 1980’s with actual patients and with the Egyptian study I referenced in the ASHRAE Journal article (“Air Distribution in the OR”, December, 2013). This is to say, we are convinced that a properly designed air curtain system will provide the safest form of air distribution in a hospital setting.

BTW - Stay tuned to the Krueger website for exciting clean room developments soon to be released!